There’s a disconnect between where you define the headers and where you use them. Your request.get uses the function’s parameter header and you haven’t pasted where you call it.
Your twitch_api_header being a single string with the 2 headers separated by a comma is… unusual though. request wants headers as an object (e.g.{ 'key': 'value', 'another_key': 'another_value' }). The raw HTTP ends up looking like
key: value
another_key: value